Coupling enhancement for medium with anti-ferromagnetic coupling

ABSTRACT

Laminated magnetic recording medium with two Co-containing layers separated by a non-magnetic Ru-containing interlayer is stabilized by Ru-containing layer between the recording layers and Co-containing stabilization layers through anti-ferromagnetic coupling. The insertion of Co layer beneath Ru spacer has resulted in increased coupling, and further coupling enhancement is achieved by low pressure process of Co and Ru layers.

RELATED APPLICATIONS

This application claims priority from Provisional Application Ser. No.60/372,353 filed Apr. 10, 2002, entitled “Enhanced anti-ferromagneticcoupling through novel process,” the entire disclosure of which ishereby incorporated herein by reference.

FIELD OF INVENTION

This invention relates to magnetic recording media, such as thin filmmagnetic recording disks, and to a method of manufacturing the media.The invention has particular applicability to high areal densitylongitudinal magnetic recording media having very low medium noise andhigh degree of thermal stability, and more particularly, to a laminatedmedium with anti-ferromagnetic (AF) coupling.

BACKGROUND

The increasing demands for higher areal recording density imposeincreasingly greater demands on thin film magnetic recording media interms of coercivity (Hc), remanent coercivity (Hcr), magnetic remanance(Mr), which is the magnetic moment per unit volume of ferromagneticmaterial, coercivity squareness (S*), signal-to-medium noise ratio(SMNR), and thermal stability of the media. These parameters areimportant to the recording performance and depend primarily on themicrostructure of the materials of the media. For example, as the SMNRis reduced by decreasing the grain size or reducing exchange couplingbetween grains, it has been observed that the thermal stability of themedia decreases.

The requirements for high areal density, i.e., higher than 30 Gb/in²,impose increasingly greater requirements on magnetic recording media interms of coercivity, remanent squareness, medium noise, track recordingperformance and thermal stability. It is difficult to produce a magneticrecording medium satisfying such demanding requirements, particularly ahigh-density magnetic rigid disk medium for longitudinal andperpendicular recording.

As the storage density of magnetic recording disks has increased, theproduct of Mr and the magnetic layer thickness t has decreased and Hcrof the magnetic layer has increased. This has led to a decrease in theratio Mrt/Hcr. To achieve a reduction in Mrt, the thickness t of themagnetic layer has been reduced, but only to a limit because themagnetization in the layer becomes susceptible to thermal decay. Thisdecay has been attributed to thermal activation of small magnetic grains(the super-paramagnetic effect). The thermal stability of a magneticgrain is to a large extent determined by K_(u)V, where K_(u) is themagnetic anisotropy constant of the magnetic layer and V is the volumeof the magnetic grain. As the magnetic layer thickness is decreased, Vdecreases. Thus, if the magnetic layer thickness is too thin, the storedmagnetic information might no longer be stable at normal disk driveoperating conditions.

The increase in K_(u) is limited to the point where the coercivityH_(c), which is approximately equal to K_(u)/Mr, becomes too large to bewritten by a conventional recording head. On the other hand, a reductionin Mr of the magnetic layer for a fixed layer thickness is limited bythe coercivity that can be written. Increasing V by increasinginter-granular exchange can also increase thermal stability. However,this approach could result in a reduction in the SMNR of the magneticlayer.

Some attempts have been made to solve the above-mentioned problem ofthermal stability. For example, U.S. Pat. No. 5,462,796 (Teng) teaches alaminated longitudinal magnetic recording medium with Cr-containingnon-magnetic layer between two magnetic layers. This medium exhibits alower medium noise than that of a medium without the Cr-containinginterlayer. However, when the medium Mrt is below 0.6 memu/cm², thelaminated medium has very poor thermal stability, which will be shownbelow. As recording density increases to about 30 Gb/in², medium Mrt hasbeen reduced to about 0.35 memu/cm². Regular laminated medium can not beused in such low Mrt regime due to thermal stability issue.

In order to squeeze as much digital information as possible on arecording disc medium there is a need to find a film structure, whichcan benefit the low noise feature of laminated medium, but hasacceptable thermal stability. Furthermore, in order to obtain highenough signal output, and reduce the medium noise of the medium withanti-ferromagnetic stabilization layers, further improvement of themedium is necessary.

SUMMARY OF THE INVENTION

Applicants found that the anti-ferromagnetic interactions of twoCo-containing magnetic layers separated by a non-magnetic interlayersuch as a Ru layer at appropriate thickness and a magnetic layer havinga higher magnetic density than that of the two Co-containing magneticlayers, e.g., a Co layer, result in enhanced anti-ferromagneticcoupling.

One embodiment is a fabrication of the thin film recording media withanti-ferromagnetic coupling with an intermediate layer produced by DCmagnetron sputtering using various inert gas species—Ar, Kr and Xe. Themedia of a preferred embodiment with a Co/Ru layer fabricated in Kr orXe gases showed stronger AF coupling. In addition, sputtering processeswith very low gas pressure produced increased coupling. Theseimprovements in AF were contributed to reduced interfacial roughness andinterlayer diffusion. Another embodiment is a method of manufacturing arecording media with improved AF coupling.

Yet, another embodiment is a magnetic recording medium, comprising apair of magnetic recording layers separated by means for improving theanti-ferromagnetic coupling of said pair of Co-containing magneticlayers. In this invention, “means for improving the anti-ferromagneticcoupling of said pair of Co-containing magnetic layers” includesembodiments shown, including interlayers of Co and Ru, and combinationsthereof or equivalents thereof.

As will be realized, this invention is capable of other and differentembodiments, and its details are capable of modifications in variousobvious respects, all without departing from this invention.Accordingly, the drawings and description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a magnetic disk drive.

FIG. 2 is a schematic representation of the film structure in accordancewith a magnetic recording medium of the prior art.

FIG. 3 is a schematic representation of the film structure of alaminated medium with anti-ferromagnetic layers in accordance with anembodiment of this invention.

FIG. 4 is a schematic representation of the film structure of alaminated medium with anti-ferromagnetic layers in accordance with anembodiment of this invention.

FIG. 5 shows the M(H) loop of the sample of Comparative Example 1.

FIG. 6 shows the M(H) loop of the sample of Example 4.

DESCRIPTION

Magnetic discs and disc drives provide quick access to vast amounts ofstored formation. Both flexible and rigid discs are available. Data onthe discs is stored circular tracks and divided into segments within thetracks. Disc drives typically employ one or more discs rotated on acentral axis. A magnetic head is positioned over the disc surface toeither access or add to the stored information. The heads for discdrives are mounted on a movable arm that carries the head in very closeproximity to the disc over the various tracks and segments.

FIG. 1 shows the schematic arrangement of a magnetic disk drive 10 usinga rotary actuator. A disk or medium 11 is mounted on a spindle 12 androtated at a predetermined speed. The rotary actuator comprises an arm15 to which is coupled a suspension 14. A magnetic head 13 is mounted atthe distal end of the suspension 14. The magnetic head 13 is broughtinto contact with the recording/reproduction surface of the disk 11. Avoice coil motor 19 as a kind of linear motor is provided to the otherend of the arm 15. The arm 15 is swingably supported by ball bearings(not shown) provided at the upper and lower portions of a pivot portion17.

A cross sectional view of a longitudinal recording disk medium isdepicted in FIG. 2. A longitudinal recording medium typically comprisesa non-magnetic substrate 20 having sequentially deposited on each sidethereof an underlayer 21, 21′, such as chromium (Cr) or Cr-containing, amagnetic layer 22, 22′, typically comprising a cobalt (Co)-base alloy,and a protective overcoat 23, 23′, typically containing carbon.Conventional practices also comprise bonding a lubricant topcoat (notshown) to the protective overcoat. Underlayer 21, 21′, magnetic layer22, 22′, and protective overcoat 23, 23′, are typically deposited bysputtering techniques. The Co-base alloy magnetic layer deposited bytechniques normally comprises polycrystallites epitaxially grown on thepolycrystal Cr or Cr-containing underlayer.

A longitudinal recording disk medium is prepared by depositing multiplelayers of films to make a composite film. In sequential order, themultiple layers typically comprise a non-magnetic substrate, one or moreunderlayers, one or more magnetic layers, and a protective carbon layer.Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr)alloy magnetic layer is deposited on a chromium or chromium-alloyunderlayer.

Methods for manufacturing a longitudinal magnetic recording medium witha glass, glass-ceramic, Al or Al—NiP substrate may also compriseapplying a seedlayer between the substrate and underlayer. A seedlayerseeds the nucleation of a particular crystallographic texture of theunderlayer. Conventionally, a seedlayer is the first deposited layer onthe non-magnetic substrate. The role of this layer is to texture(alignment) the crystallographic orientation of the subsequentCr-containing underlayer, and might also produce small grain size, whichis desired for the purpose of reducing recording noise.

The seedlayer, underlayer, and magnetic layer are conventionallysequentially sputter deposited on the substrate in an inert gasatmosphere, such as an atmosphere of argon. A carbon overcoat istypically deposited in argon with nitrogen, hydrogen or ethylene.Lubricant topcoats are typically about 20 Å thick.

A substrate material conventionally employed in producing magneticrecording rigid disks comprises an aluminum-magnesium (Al—Mg) alloy.Such Al—Mg alloys are typically electrolessly plated with a layer of NiPat a thickness of about 15 microns to increase the hardness of thesubstrates, thereby providing a suitable surface for polishing toprovide the requisite surface roughness or texture.

Other substrate materials have been employed, such as glass, e.g., anamorphous glass, glass-ceramic material that comprises a mixture ofamorphous and crystalline materials, and ceramic materials.Glass-ceramic materials do not normally exhibit a crystalline surface.Glasses and glass-ceramics generally exhibit high resistance to shocks.

A magnetic material is composed of a number of submicroscopic regionscalled magnetic grains. Each grain contains parallel atomic magneticmoments and is always magnetized to saturation (Ms), but the directionsof magnetization of different grains are not necessarily parallel. Inthe absence of an applied magnetic field, adjacent grains may beoriented randomly in any number of several directions, called thedirections of easy magnetization, which depend on the geometry of thecrystal, stress, etc. The resultant effect of all these variousdirections of magnetization may be zero, as is the case with anunmagnetized specimen. When a magnetic field is applied, the grains willhave their moment align parallel to the direction of the applied fieldwhen the applied field is sufficiently high for this magnetic grain,until all grains are aligned to the same direction, and the materialreaches the point of saturation magnetization.

The ease of magnetization or demagnetization of a magnetic materialdepends on the crystalline structure, grain orientation, the state ofstrain, and the direction of the magnetic field. The magnetization ismost easily obtained along the easy axis of magnetization but mostdifficult along the hard axis of magnetization. A magnetic material issaid to possess a magnetic anisotropy when easy and hard axes exist. Onthe other hand, a magnetic material is said to be isotropic when thereare no easy or hard axes. A magnetic material is said to possess auniaxial anisotropy when the easy axis is oriented along a singlecrystallographic direction, and to possess multiaxial anisotropy whenthe easy axis aligns with multiple crystallographic directions.

“Anisotropy energy” is the work against the anisotropy force to turnmagnetization vector away from an easy direction. For example, a singlecrystal of iron, which is made up of a cubic array of iron atoms, tendsto magnetize in the directions of the cube edges along which lie theeasy axes of magnetization. A single crystal of iron requires about1.4×10⁵ ergs/cm³ (at room temperature) to move magnetization from aneasy direction into the hard axis of magnetization, which is along acubic body diagonal.

The anisotropy energy U_(A) could be expressed in an ascending powerseries of the direction cosines between the magnetization and thecrystal axes. For cubic crystals, the lowest-order terms take the formof Equation (1),U _(A) =K ₁(α₁ ²α₂ ²+α₂ ²α₃ ²+α₃ ²α₁ ²)+K ₂(α₁ ²α₂ ²α₃ ²)  (1)where α₁, α₂ and α₃ are direction cosines with respect to the cubicaxes, and K₁ and K₂ are temperature-dependent parameters characteristicof the material, called anisotropy constants.

Anisotropy constants can be determined from (1) analysis ofmagnetization curves, (2) the torque on single crystals in a largeapplied field, and (3) single crystal magnetic resonance. The term“anisotropy constant” is often referred to as magnetocrystallineanisotropy constant.

While Equation (1) applies for a cubic lattice, similar equations arealso known for other lattice systems. For example, for a hexagonal closepacked (HCP) lattice, the equation for U_(A) is the following:U _(A) =K ₁ sin² θ+K₂ sin⁴ θ  (2)where θ is the angle between the Ms vector, i.e., the saturationmagnetization direction, and the c axis (easy axis), and K_(1 and K) ₂are anisotropy constants.

The magnetic anisotropy of longitudinal and perpendicular recordingmedia makes the easily magnetized direction of the media located in thefilm plane and perpendicular to the film plane, respectively. Theremanent magnetic moment of the magnetic media after magnetic recordingor writing of longitudinal and perpendicular media is located in thefilm plane and perpendicular to the film plane, respectively.

For thin film longitudinal magnetic recording media, the desiredcrystalline structure of the Co and Co alloys is HCP with uniaxialcrystalline anisotropy and a magnetization easy direction along thec-axis lies in the plane of the film. The better the in-plane c-axiscrystallographic texture, the higher the magnetic remanance of the Coalloy thin film used for longitudinal recording. For very small grainsizes coercivity increases with increased grain size. As grain sizeincreases, noise increases. To achieve a low noise magnetic medium, theCo alloy thin film should have uniform small grains with grainboundaries that can efficiently isolate neighboring grain to reducemedium noise. This kind of microstructure and crystallographic textureis normally achieved by manipulating the deposition process, or mostoften by the proper use of an underlayer.

The linear recording density can be increased by increasing the Hr ofthe magnetic recording medium, and by decreasing the medium noise, as bymaintaining very fine magnetically non-coupled grains. Medium noise inthin films is a dominant factor restricting increased recording densityof high-density magnetic hard disk drives, and is attributed primarilyto inhomogeneous grain size and intergranular exchange coupling.Accordingly, in order to increase linear density, medium noise must beminimized by suitable microstructure control.

The recording media of the invention may be a rigid magnetic discrotatable about an axis that is incorporated into a disc drive shown inFIG. 1. Disc drives such as this are standard equipment in the industry.See, Mee, C. D. and Daniel, E. D., MAGNETIC RECORDING, Vols. I-III(McGraw-Hill pub. 1987); F. Jorgenson, The Complete Handbook of MagneticRecording, Chapter 16 (3rd. ed. 1988), and U.S. Pat. No. 5,062,021, therelevant disclosures of which are incorporated herein by reference. Themagnetic recording media of the present invention may also be used withflexible magnetic discs or tapes using known flexible substrates.

This invention provides magnetic recording media suitable for high arealrecording density exhibiting high thermal stability and high SMNR. Thisinvention achieves such technological advantages by providing (1) aRu-containing layer between two Co-containing magnetic layers, one ofthe Co-containing magnetic layers being a magnetic recording layer andthe other being a stabilization layer, and (2) a very thin Cohexagonal-structured layer in between the bottom magnetic stabilizationlayer and Ru spacer, and (3) the novel process to produce this Cointermediate and Ru spacer layers so that much larger exchange energy isachieved for maximum thermal stability advantage. In this application,word “containing,” for example in Ru-containing, means that the layercomprises the elements or compounds before the word “containing” but thelayer could still include other elements and compounds.

The ratio K_(u)V/k_(B)T determines the thermal stability of magneticrecording media. In another words, it estimates the signal decay of themagnetic recording media. In the above ratio, K_(u) is an anisotropyconstant defined by the equation K_(u)=K₁+2K₂, wherein K₁ and K₂ are theanisotropy constants of Equation (2), V is the volume of magneticswitching units, which can approximately be represented by magneticgrains, K_(B) is Boltzman's constant and T is temperature in Kelvin.

Lu and Charap, “Thermal instability at 10 Gbit/in² magnetic recording,”IEEE TRANSACTION ON MAGNETICS, Vol. 30, No. 6, pp. 4230-4232, November1994, discloses that K_(u)V/k_(B)T must be at least 60 in order for thewritten bits to be marginally stable. In one embodiment, a high magneticdensity layer, preferably, a Co layer and a non-magnetic layer,preferably, a Ru-containing layer, together are included between a firstCo-containing recording layer and a second Co-containing recordinglayer. The term “high magnetic density layer” refers to a layer having ahigher magnetic density than that of the Co-containing recording layers.

FIGS. 3 and 4 show the film structures of two embodiments of thisinvention. FIG. 3 shows a underlayer 39 (typically, Cr-containing)deposited on a substrate. Sequentially, from the top of the filmstructure of FIG. 3 to the underlayer 39 are a carbon overcoat 31, a1^(st) Co-containing recording layer 32, a Ru layer 33, a high magneticdensity layer 34, e.g., a Co layer, and a 2^(nd) Co-containing recordinglayer 36. In one embodiment, the underlayer causes the easy axis of the2^(nd) Co-containing recording layer 36 to be in-plane through epitaxialgrowth. Another embodiment of this invention is shown in FIG. 4. Theremay be multiple Ru layers and multiple Co layers between theCo-containing recording layers.

The Co-containing recording layer can comprise any Co-based alloy suchas CoCrPt, CoCrPtTa, CoCrPtTaNb, CoCrPtB. Each recording layer can besingle magnetic layer or dual magnetic layers immediately adjacent toeach other. The alloy of the 2^(nd) Co-containing recording layer may ormay not be the same as the alloy of the 1^(st) recording layer. Thethickness of each recording layer can be in the range of 0.5 nm to 12 nmwith the 1^(st) recording layer to be sufficiently thick to provideenough signal. The Ru layer thickness is about 0.6 to 1.2 nm, and shouldbe optimized to obtain optimal anti-ferromagnetic coupling of the twolayers adjacent to it.

The high magnetic density layer, preferably a Co layer, can have athickness from about 0 to 20 Å, and comprise any kind of Co-based alloywith high Ms. The edge length of the base plane of the lattice of ahexagonal structure is “a.” The distance between two base planes of thelattice of a hexagonal structure is “c.” When the absolute values of therelevant difference of “a” values of two hexagonal structures and theabsolute value of the relevant difference of “c” values of two hexagonalstructures are both less than 6%, it means that these two structureshave “similar lattice constants.”

In a variation, there could further be a subseedlayer and a seedlayer ofabout 1.0 nm to 160 nm thickness each below the underlayer 39 tonucleate growth. A portion of the subseedlayer, the seedlayer and/or theunderlayer could be oxidized by being sputter deposited with Ar andoxygen to promote a decrease in grain size. The term “a portion of” isdefined herein to include all or part of a layer. Therefore, the entirelayer, i.e., extending from one end of the layer to the opposite end ofthe layer may be in the oxidized form.

The carbon overcoat in FIGS. 3 and 4 could be further coated with alubricant layer generally 1 nm to 3 nm thick. The lubricant ispreferably a fluoro-chlorocarbon or a perfluoroether. Examples includeCCl₂FCClF₂, CF₃(CF₂)₄CF₃, CF₃(CF₂)₅CF₃, CF₃(CF₂)₁₀CF₃, andCF₃(CF₂)₁₆CF₃.

The substrates that may be used in the invention include glass,glass-ceramic, aluminum/NiP, metal alloys, plastic/polymer material,ceramic, glass-polymer, composite materials or other non-magneticmaterials.

The underlayer in FIGS. 3 and 4 may form a (112) orientation whendeposited on a B2 structured seedlayer such as NiAl. Then, a magneticlayer having a substantially Co(10.0) crystallographic orientation couldbe deposited on the underlayer. The underlayers shown in FIGS. 3 and 4may also form a (200) orientation when deposited on Al/NiP substrates.Then, a magnetic layer having a substantially Co(11.0) crystallographicorientation could be deposited on the underlayer.

Desirably, the lattice constant and the crystal plane of the seedlayer,if used, should closely match that of the underlayer. As a consequenceof lattice and crystalline plane matching, the magnetic layer will growin a close-packed hexagonal structure with a Co(10.0) or Co(11.0)crystallographic orientations predominantly parallel to the film planewith the magnetic easy axis, c-axis, lying predominantly in the filmplane.

In a preferred embodiment, the thickness of the BCC structure seedlayercould be about 0 Å to about 150 Å, preferably between about 20 Å andabout 80 Å, and most preferably about 40 Å. The thickness of theunderlayer could be about 20 Å to about 150 Å, preferably between about20 Å and about 80 Å, and most preferably about 45 Å. The thickness ofthe recording layer could be about 40 Å to about 250 Å, preferablybetween about 60 Å and about 200 Å, and most preferably about 100-160 Å.The thickness of the stabilization layer could be about 10 Å to about 50Å, preferably between about 15 Å and about 45 Å, and most preferablyabout 20-40 Å. The thickness of the Ru-containing layer could be about 6Å to about 12 Å, preferably between about 7 Å and about 9 Å, and mostpreferably about 8 Å. The thickness of the interlayer (optional) belowthe magnetic layers could be about 5 Å to about 50 Å, preferably betweenabout 15 Å and about 40 Å, and most preferably about 15-25 Å. Thethickness of the protective layer could be about 20 Å to about 300 Å,preferably between about 25 Å and 50 Å, and most preferably about 30 Å.The protective layer could be made of hydrogenated carbon (CH_(x)),nitrogenated carbon (CN_(x)), hybrid carbon (CH_(x)N_(y)), or acombination of these.

The magnetic recording medium has a remanent coercivity of about 2000 toabout 10,000 Oersted, and an Mrt (product of remanance, Mr, and magneticlayer thickness, t) of about 0.1 to about 2.0 memu/cm². In a preferredembodiment, the coercivity is about 2500 to about 9000 Oersted, morepreferably in a range of about 3000 to about 7000 Oersted, and mostpreferably in a range of about 4000 to about 5500 Oersted. In apreferred embodiment, the Mrt is about 0.20 to about 1 memu/cm², morepreferably in a range of about 0.20 to about 0.5 memu/cm², and mostpreferably in a range of about 0.25 to about 0.45 memu/cm².

In certain embodiments, applicants investigated three types of inert gasspecies—Ar, Kr, and Xe for the sputtering of thin Co and Ru interlayers(also called spacer layers), with the former contributing to theenhancement of the coupling, and latter at the appropriate thickness(around 8 Å) providing the most advantageous spacing for AF couplingbetween the magnetic layers below and above it. Furthermore, differentprocess windows were investigated. In particular, applicants have foundthat low-pressure (less than 5 mTorr) process could improve theinterface quality and result in further increase of AF coupling betweenthe identical magnetic films.

EXAMPLES

The films were sputtered on NiP-plated Al substrates in a DC magnetronsputtering apparatus. The film structure produced and analyzed wasCr/CrW/(CoCrPtB)¹/(CoCrPtB)²/Co/Ru/(CoCrPtB)³/C, wherein thesuperscripts denote the layer number of the CoCrPtB-containing layers.

Specifically, the film structure and compositions wereCr/Cr₉₀W₁₀/Co₇₇Cr₈Pt₇B₈/Co₆₄Cr₁₂Pt₆B₈/Co/Ru/Co₆₁Cr₁₅P₁₂B₁₂/C, whereinall the numbers are in atomic percentage. The AF coupling is consideredto is mainly from (CoCrPtB)¹, (CoCrPtB)², Co and (CoCrPtB)³ magneticlayers, wherein (CoCrPtB)¹, (CoCrPtB)² and (CoCrPtB)³ magnetic layersare coupled unidirectionally by the high magnetic density material Cointerposed between the two magnetic layers, thereby allowing enhancedintergranular exchange coupling. Such a structure allows designers theability and flexibility to use high anisotropy, high magnetizationmaterials that are capable of high exchange coupling in a multilayerstructure.

The base pressure typically was maintained in the range of high digitsof 10⁻⁸ Torr. The substrates were preheated to around 300° C., and thesputtering pressure was in the range of 1 to 6.1 mTorr. All the metalfilms were sputtered in Ar gas, with the exception of Co/Ru layers whichwere produced in Ar, Kr and Xe gases for comparison, and with nominal(about 6.1 mTorr) and low (less than 6.1 mTorr) pressures.

The basic magnetic properties of these media were tested on anon-destructive rotating disc magnetometer. The recording signal andmedia noise were measured at 600 kfci linear density using a Guziktester with a giant magnetoresistive (GMR) head that flies at the heightof 0.3 μinch. The M(H) loops were obtained from a Vibrating SampleMagnetometer (VSM).

Table 1 shows the results of 7 samples of which there are threecomparative examples and four examples. The process gas type andpressure for producing Co/Ru layers, the equalized SMNR, as well asexchange coupling strength are tabulated in Table 1. Comparative Example1 does not have a Co interface layer. 6.1 mTorr refers to the nominalprocess pressure. For Ar, Kr and Xe, the lowest pressure to start plasmafor Co and Ru sputtering was found to be in the range from 1.4 to 3.6mTorr.

The data in Table 1 shows that AF coupling increased due to thecoupling-enhancing Co layer (see Comparative Example 1 and Example 1).Furthermore, for each gas, when the gas pressure was reduced, AFcoupling increased by 5 to 20% as compared to the results in which Coand/or Ru were deposited at the nominal 6.1 m Torr. The low pressure Krprocessed sample (Example 4) possessed the highest coupling of 0.125erg/cm².

FIGS. 5 and 6 show the M(H) loops for samples Comparative Example 1 andExample 4, respectively. These figures clearly show the increasedcoupling of the sample of Example 4 as compared to Comparative Example1, from the increase of both first switching field from 500 to 700 Oe,and the switched magnetization moment of 1.2 to 1.8×10⁻⁴ emu.

Meanwhile, the recording performance was preserved as shown by eSMNRvalues in Table 1. The basic magnetic properties—Her, Mrt and S*—weresimilar among the Examples 1-4, while the sample of Comparative Example1 had slightly higher net Mrt due to less AF coupling.

The improvement of AF coupling with the preservation of recordingcharacteristics is presumably due to the minimized surface andinterfacial roughness. Heavier noble gas atoms will have reduced recoilenergy at the target surface, and while a substrate bias is applied, atnear the substrate as well. Therefore, low pressure of the gas in the Coand/or Ru deposition chamber reduces the scattering of sputteredmaterials so that smoother and denser films are formed. When lowpressure was used for producing these films, a combination of scatteringminimization as well as electron heating resulted in better quality ofultra thin films and surfaces/interfaces.

The AF coupling was evaluated by measuring Jex, the exchange energydensity of the system, which represents the strength ofantiferromagnetic coupling between two magnetic layers. The method fordetermining Jex was as follows. VSM (vibrating sample magnetometer) wasused to measure remanance loop of a sample (cut into a small piece) inthe longitudinal direction of sample to determine the field for firstswitch of remanance, which is Hex. Then, the magnetization that isswitched, M, was determined. Jex was calculated by the formula:Jex=Hex*M/(2*A), wherein A is the area of the sample, Hex is in the unitof Oe, M is in the unit of emu, A is in the unit of cm² and Jex is inthe unit of erg/cm².

TABLE 1 Samples listed with process gas, pressure, eSMNR and AF couplingJex Gas Co pressure Ru pressure eSMNR Jex Sample Type (mTorr) (mTorr)(dB) (erg/cm2) CE 1* Ar 6.1 17.9 0.060 CE 2 Ar 6.1 6.1 17.9 0.094 CE 3Xe 6.1 6.1 17.4 0.091 E 1 Ar 3.6 1.9 18.1 0.101 E 2 Xe 2.2 2.2 17.80.104 E 3 Kr 6.1 6.1 17.8 0.104 E 4 Kr 2.4 1.4 17.7 0.125 *CE =Comparative Example **E = Example

Applicants found that the usage of Kr and Xe gases for Co and/or Rulayer sputtering, and a mixture gas of Kr and Ar, or Xe and Ar, or Krand Xe, results in enhanced exchange coupling in media with AFCstructure. Applicants also found that low pressure sputtering (less than6 mTorr, preferably less than 5 mTorr) to the lowest gas pressure limitthat the plasma could be generated and sustained is preferable.Furthermore, substrate bias during the sputtering of Co and/or Ru layerscould be used for tuning magnetic properties. Applicants found that thesubstrate could be Al dominated conductive type, or glass, glass ceramictype, with appropriate seedlayer and/or underlayer and/or intermediatelayer structure to establish crystallographic orientation and grainstructure. The magnetic alloys could be Co alloys with at least oneelement from a collection of Cr, Pt, B, Ta, Nb, Si, etc. The magneticlayers for storage and AF coupling could be single layers on top andbelow Co/Ru films, or multiple adjacent layers, or laminated structurewith thin non-magnetic spacing.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

This application discloses several numerical range limitations. Personsskilled in the art would recognize that the numerical ranges disclosedinherently support any range within the disclosed numerical ranges eventhough a precise range limitation is not stated verbatim in thespecification because this invention can be practiced throughout thedisclosed numerical ranges. A holding to the contrary would “let formtriumph over substance” and allow the written description requirement toeviscerate claims that might be narrowed during prosecution simplybecause the applicants broadly disclose in this application but thenmight narrow their claims during prosecution. Finally, the entiredisclosure of the patents and publications referred in this applicationare hereby incorporated herein by reference.

1. A magnetic recording medium, comprising a first Co-containing layerand a second Co-containing layer separated by a non-magnetic interlayerand a magnetic interlayer, wherein the magnetic interlayer has a highermagnetic density than that of the first and second Co-containing layersand the magnetic recording medium has Jex of 0.1 erg/cm² or more,wherein the magnetic recording medium comprisesCr/Cr₉₀W_(l0)/Co₇₇Cr₈Pt₇B₈/Co₆₄Cr₁₂Pt₆B₈/Co/Ru/Co₆₁Cr₁₅Pt₁₂B ₁₂/C.
 2. Amagnetic recording medium, comprising Cr/CrW/(CoCrPtB)¹/(CoCrPtB)²/CoRu/(CoCrPtB)³/C layers, wherein the superscripts denote the layer numberof the CoCrPtB-containing layers, the magnetic recording medium has Jexof 0.1 erg/cm², and wherein (CoCrPtB)¹ is in direct contact with(CoCrPtB)² or more.